CHICAGO — On a bleak stretch of road outside a Burger King four years ago, a white police officer opened fire on a black teenage boy. Captured on a dashboard camera, the killing reshaped Chicago.

The officer, Jason Van Dyke, became the city’s first patrolman in almost 50 years to be convicted of murder. The teenager, Laquan McDonald, became a national symbol of police brutality. The city’s police department, one of the country’s largest, was overhauled. And the powerful mayor, battered by the fallout, stunned Chicago by announcing he would not run again.

On Friday, Mr. Van Dyke, an officer no longer, was sentenced to just shy of seven years in an Illinois prison for second-degree murder and 16 counts of aggravated battery with a firearm, one for every bullet he fired on that October night in 2014. Though an appeal is possible, the sentence provided a measure of finality in a case that dominated Chicago’s news cycles for years, laying bare this city’s racial divisions and upending its government.

But the final chapter left few people satisfied.

Laquan’s great-uncle, the Rev. Marvin Hunter, said it was a qualified victory that a police officer was going to prison for murder. But he said the sentence was far too short, and reduced Laquan to “a second-class citizen.”

William Calloway, an activist who had pressed for the release of the video in 2015, said that he was “heartbroken” by the sentence of 81 months.

Mr. Van Dyke “deserves to spend the rest of his life behind bars,” he said. “That’s a slap in the face to us and a slap on the wrist to him.”